I was pretty sad to see the pattern matching PR reverted for 7.1 [0], but I guess the Rails team wants to make sure they nail the execution (?) even if that means being late to the pattern matching party, which is arguably one of the best additions to Ruby since the 1.9.3 hash syntax.
For now, I'm good with the little gem that kddnewton put together (https://github.com/kddnewton/rails-pattern_matching).
[0]: https://github.com/rails/rails/pull/45553